Zoom lens

ABSTRACT

A zoom lens includes a first lens group with a negative refractive power, a second lens group with a positive refractive power, and an aperture stop disposed in and movable with the second lens group. Each of the first lens group and the second lens group moves individually. The zoom lens further includes a doublet lens disposed on a first side of the aperture stop and between the first lens group and the aperture stop, and at most two lenses including at least one aspheric lens are disposed on a second side of the aperture stop.

BACKGROUND OF THE INVENTION a. Field of the Invention

The invention relates generally to an optical lens, and moreparticularly to a zoom lens.

b. Description of the Related Art

With the advances in optical-electronic technologies, image-sensingdevices such as a projector, a digital video camera and a digital camerahave been widely used in daily life. A zoom lens that functions as a keycomponent for an image-sensing device can, through zooming and focusingadjustments, precisely focus an object image on a screen or CCD, andthus the performance of the zoom lens is closely related to the imagequality. Nowadays, there is a growing need for fabricating ahigh-performance, compact, light and low-cost zoom lens to maintaincompetitive advantage. Accordingly, it is desirable to provide a zoomlens that has a reduced size, a large aperture stop, low aberrations,inexpensive prices, high performance and high resolution.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present disclosure, a zoom lens includesa first lens group with a negative refractive power, a second lens groupwith a positive refractive power, and an aperture stop disposed in andmovable with the second lens group. Each of the first lens group and thesecond lens group moves individually. The zoom lens further includes adoublet lens disposed on a first side of the aperture stop and betweenthe first lens group and the aperture stop, and at most two lensesincluding at least one aspheric lens are disposed on a second side ofthe aperture stop.

According to the above embodiment, the zoom lens may have at least onedoublet lens to balance chromatic aberration, and may have at least oneaspheric lens to reduce aberration. Besides, the zoom lens may have areduced number of total lenses and a large aperture stop. Further, thezoom lens may have a smaller value of EXP to reduce the total tracklength and thus is favorable for miniaturization, where Exp denotes adistance from an intersection to an image plane of a light valve, andthe intersection is formed by an optical axis of the zoom lens crossedby a chief ray emerging from a designated point of a periphery of thelight valve. Accordingly, the zoom lens is featured with good correctionability, reduced size, and improved image qualities.

Other objectives, features and advantages of the invention will befurther understood from the further technological features disclosed bythe embodiments of the invention wherein there are shown and describedpreferred embodiments of this invention, simply by way of illustrationof modes best suited to carry out the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram illustrating a zoom lens respectivelyin a wide-angle position and in a telephoto position according to anembodiment of the invention.

FIG. 2 shows a schematic diagram illustrating a zoom lens respectivelyin a wide-angle position and in a telephoto position according toanother embodiment of the invention.

FIG. 3 shows a schematic diagram illustrating a zoom lens respectivelyin a wide-angle position and in a telephoto position according toanother embodiment of the invention.

FIG. 4 shows a schematic diagram illustrating a zoom lens respectivelyin a wide-angle position and in a telephoto position according toanother embodiment of the invention.

FIG. 5 shows a schematic diagram illustrating a zoom lens respectivelyin a wide-angle position and in a telephoto position according toanother embodiment of the invention.

FIGS. 6-10 respectively show modulation transfer function curves of zoomlenses of FIGS. 1-5 in the wide-angle position.

FIGS. 11-15 respectively show MTF curves of zoom lenses of FIGS. 1-5 inthe wide-angle position.

FIGS. 16-20 respectively illustrate astigmatic field curves andpercentage distortion curves of zoom lenses of FIGS. 1-5 under differentwavelengths of light.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiments,directional terminology, such as “top,” “bottom,” “front,” “back,” etc.,is used with reference to the orientation of the Figure(s) beingdescribed. The components of the invention can be positioned in a numberof different orientations. As such, the directional terminology is usedfor purposes of illustration and is in no way limiting. Further,“First,” “Second,” etc, as used herein, are used as labels for nounsthat they precede, and do not imply any type of ordering (e.g., spatial,temporal, logical, etc.). Besides, though the following embodiments onlydescribe the application environment using projection devices anddisplay systems, the invention, however, is not limited thereto. Thefollowing embodiments of a zoom lens may be applied to any system orenvironment according to actual demands.

According to an embodiment of the invention, a zoom lens includes afirst lens group with a negative refractive power, a second lens groupwith a positive refractive power, and an aperture stop disposed in andmovable with the second lens group. Each of the first lens group and thesecond lens group moves individually. The zoom lens further includes adoublet lens disposed on a first side of the aperture stop and betweenthe first lens group and the aperture stop, and at most two lensesincluding at least one aspheric lens are disposed on a second side ofthe aperture stop. The zoom lens may satisfy one of the followingconditions: (1) the first lens group comprises two meniscus lenses witha negative refractive power, the second lens group comprises two lenseswith a positive refractive power located between the two meniscus lensesand the first doublet lens, and the aspheric lens has a positiverefractive power; (2) the first lens group comprises a meniscus lenswith a negative refractive power and an aspheric lens, the second lensgroup comprises a meniscus lens with a negative refractive power locatedbetween the first lens group and the first doublet lens, and eachaspheric lens in the first lens group and the second lens group has apositive refractive power; (3) the first lens group comprises twomeniscus lenses with a negative refractive power, the second lens groupcomprises a biconvex lens with a positive refractive power and a seconddoublet lens, the biconvex lens and the second doublet lens are locatedbetween the first lens group and the first doublet lens, and theaspheric lens of the second lens group has a positive refractive power.

According to another embodiment of the invention, a zoom lens includes afirst lens group and a second lens group arranged in order along adirection, an aperture stop disposed in the second lens group, and adoublet lens disposed on a first side of the aperture stop and betweenthe first lens group and the aperture stop, and at least one asphericlens disposed on a second side of the aperture stop. Each of the firstlens group and the second lens group moves individually. The zoom lensfurther satisfies the condition: −26 mm≤EXP≤−28.5 mm, where Exp denotesan exit pupil position that is measured as a distance from anintersection to an image plane of a light valve, and the intersection isformed by an optical axis of the zoom lens crossed by a chief rayemerging from a designated point of a periphery of the light valve. Inan optical projection system, the image plane of a light valve istypically located in an object side of an optical lens but not an imageside for projection of the optical lens. In case the zoom lens isdesigned to meet the condition of EXP<−28.5 mm, it may result in anexcess long total track length and thus is difficult to miniaturize theentire lens assembly. In comparison, in case the zoom lens is designedto meet the condition of EXP>−26 mm, it may result in an excess shortback focus to cause interference between illumination light and imagelight and thus worsen image qualities. In one embodiment, the doubletlens may include a lens with a positive refractive power and an index ofrefraction of smaller than 1.68.

In one embodiment, an F number of the zoom lens is no more than 2.2. Inone embodiment, a zoom ratio of the zoom lens is in the range of1.05-1.2. In one embodiment, a back focus distance of the zoom lens isin the range of 18-24 mm. In one embodiment, a throw ratio of the zoomlens in a wide-angle position is in the range of 1.3-1.6, where thethrow ratio is the ratio of a throw distance to a screen width. In oneembodiment, a total number of lenses of the zoom lens is no more thanten. In one embodiment, the aspheric lens is made from glass or plastic.

The light valve LV, which is a commonly used device, is a kind ofspatial light modulator. The light valve LV is capable of convertingillumination beams into image beams and may be a DMD, an LCD, an LCOS,etc.

According to the above embodiments, the zoom lens is featured with goodcorrection ability, reduced size, and improved image qualities.

FIG. 1 shows a schematic diagram illustrating a zoom lens respectivelyin a wide-angle position and in a telephoto position according to anembodiment of the invention. As shown in FIG. 1, a zoom lens 10 aincludes a first lens group 20, a second lens group 30 and an aperturestop 14 disposed in and movable with the second lens group 30. The firstlens group 20 and the second lens group 30 are capable of movingindividually to switch between the wide-angle position (shown in the topof FIG. 1) and the telephoto position (shown in the bottom of FIG. 1).In detail, when the first lens group 20 and the second lens group 30move towards each other, the zoom lens 10 a is switched from thewide-angle position to the telephoto position to decrease an interval d1and increase an interval d2. In comparison, when the first lens group 20and the second lens group 30 move away from each other, the zoom lens 10a is switched from the telephoto position to the wide-angle position toincrease the interval d1 and decrease the interval d2. Therefore, thezoom lens may include two lens groups, and the variable interval d1distinguishes the first lens group 20 from the second lens group 30. Inone embodiment, the first lens group 20 is movable in a direction of anoptical axis 12 for focus adjustment, and the second lens group 30 ismovable in the direction of the optical axis 12 for zooming.

The first lens group 20 has a negative refractive power, and the secondlens group 30 has a positive refractive power. The first lens group 20includes lenses L1 and L2 arranged in order, along the optical axis 12,from a magnified side (on the left of FIG. 1) to a minified side (on theright of FIG. 1). The second lens group 30 includes lenses L3, L4 L5,L6, L7 and L8 arranged in order, along the optical axis 12, from themagnified side to the minified side. The refractive powers of the lensL1, L2, L3, L4, L5, L6, L7 and L8 are negative, negative, positive,negative, positive, positive, negative and positive, respectively. Inthis embodiment, the lens L8 in the second lens group 30 nearest theminified side is an aspheric lens. The lens L6 and lens L7 are arrangedtogether as one piece to form a doublet lens with a positive refractivepower, and the aperture stop 14 is located between the lens L7 and thelens L8. In one embodiment, the lens L6 has a negative refractive powerand the lens L7 has a positive refractive power. In one embodiment, theaspheric lens is made from glass.

Note that adjoining surfaces of each two adjacent lenses in a doubletlens have an identical radius of curvature, and that the lenses in adoublet lens can be fit together by various ways. For example, thelenses may be cemented together by applying an optical adhesive on twolens surfaces facing each other or stacked and then pressed to be fittedwith each other.

In the zoom lens 10 a, the lens L1 has a convex magnified-side surfaceS1 and a concave minified-side surface S2, the lens L2 has a convexmagnified-side surface S3 and a concave minified-side surface S4, thelens L3 has a convex magnified-side surface S5 and a convexminified-side surface S6, the lens L4 has a concave magnified-sidesurface S7 and a concave minified-side surface S8, the lens L5 has aconvex magnified-side surface S9 and a convex minified-side surface S10,the lens L6 has a convex magnified-side surface S11, the lens L7 has aconcave magnified-side surface S12 and a concave minified-side surfaceS13, and the lens L8 has a concave magnified-side surface S15 and aconvex minified-side surface S16 crossed with the optical axis 12. Inthis embodiment, the surface 17 denotes a surface of a cover glass ofthe light valve (not shown). In another embodiment, the surface 17 is animage plane of the light valve (such as a DMD, an LCD or an LCOS).

The detailed optical data of the zoom lens 10 a are shown in Table 1 andTable 2 below. Note the optical data provided below are not used forlimiting the invention, and those skilled in the art may suitably modifyparameters or settings of the following embodiment with reference of theinvention without departing from the scope or spirit of the invention.

TABLE 1 Surface Radius Interval Refractive Abbe number (mm) (mm) indexnumber Object description S1 72.55 0.80 1.49 70.2 lens L1(meniscus) S224.72 4.24 S3 61.79 0.80 1.49 70.2 lens L2(meniscus) S4 29.67 d1 S5728.58 3.80 1.62 63.3 lens L3(biconvex) S6 −36.61 7.13 S7 −29.43 0.801.49 70.2 lens L4(biconcave) S8 16.50 7.82 S9 18.42 3.74 1.77 49.6 lensL5(biconvex) S10 −725.85 7.20 S11 18.10 6.00 1.62 63.3 lens L6(biconvex)S12 −11.91 1.70 1.70 30.1 lens L7(biconcave) S13 22.25 0.74 S14 ∞ 0.75aperture stop S15 −30.13 6.00 1.77 50.0 lens L8(aspheric) S16 −15.18 d2S17 ∞ cover glass surface d1 d2 wide 18.31 20.00 tele 11.66 20.92

TABLE 2 F/# EFL(mm) TTL(mm) wide 2.09 15.68 92 tele 2.17 17.72 86.27

The Symbol F/# shown in the above table is an aperture value of theaperture stop.

In the embodiments of the invention, an effective focal length of theoptical lens is denotes as “EFL”, as shown in the above table.

In the embodiments of the invention, a total track length of the opticallens is denotes as “TTL”, as shown in the above table. In thisembodiment, the total track length TTL is a distance along the opticalaxis 12 measured from the surface S1 to the surface S17, as shown in theabove table.

In the following design examples of the invention, each aspheric surfacesatisfies the following equation:

${x = {\frac{c^{\prime}y^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{\prime 2}y^{2}}}} + {Ay}^{4} + {By}^{6} + {Cy}^{8} + {Dy}^{10} + {Ey}^{12} + {Fy}^{14} + {{Gy}^{16}\mspace{14mu} \ldots}}}\mspace{11mu},$

where x denotes a sag of an aspheric surface along the optical axis 12,c′ denotes a reciprocal of a radius of an osculating sphere, k denotes aConic constant, y denotes a height of the aspheric surface measured in adirection perpendicular to the optical axis 12, and A-G are asphericcoefficients. Table 3 lists aspheric coefficients and conic constant ofeach aspheric surface of the zoom lens 10 a.

TABLE 3 K A B C D S15 3.17E+00 −1.95E−04 −1.02E−06 −1.36E−09 −4.87E−12S16 1.08E−01 −4.71E−05 −2.67E−07  5.07E−09 −4.54E−11

A zoom lens 10 b according to another embodiment including lenses L1-L7(with respective refractive power of negative, negative, positive,positive, negative, positive, positive) is described below withreference to FIG. 2. The lens L5 and lens L6 are arranged together asone piece to form a doublet lens with a negative refractive power. Theaperture stop 14 is located between the lens L6 and the lens L7. Thelens L7 is an aspheric lens and having a concave magnified-side surfaceS13 and a convex minified-side surface S14 crossed with the optical axis12. In other embodiment, the lens L5 may have a positive refractivepower and the lens L6 may have a negative refractive power. In thisembodiment, the aspheric lens is made from glass. The detailed opticaldata of the zoom lens 10 b are shown in Table 4 and Table 5, and theaspheric surface data are shown in Table 6 below.

TABLE 4 Surface Radius Interval Refractive Abbe number (mm) (mm) indexnumber Object description S1 43.73 1.00 1.58 59.4 lens L1(meniscus) S222.87 4.71 S3 90.97 1.00 1.49 70.2 lens L2(meniscus) S4 27.74 d1 S5427.37 2.88 1.62 63.3 lens L3(biconvex) S6 −38.02 3.86 S7 22.30 3.721.92 24.0 lens L4(meniscus) S8 60.00 5.42 S9 −38.35 0.80 1.81 22.8 lensL5(biconcave) S10 8.36 2.80 1.88 40.8 lens L6(meniscus) S11 25.19 0.63S12 ∞ 0.85 aperture stop S13 −36.73 5.74 1.73 40.4 lens L7(aspheric) S14−11.19 d2 S15 ∞ cover glass surface d1 d2 wide 33.66 20.45 tele 27.6521.53

TABLE 5 F/# EFL(mm) TTL(mm) wide 2 15.7 89.67 tele 2.08 17.29 84.74

In this embodiment, the total track length TTL is a distance along theoptical axis 12 measured from the surface S1 to the surface S15.

TABLE 6 K A B C D E S13 0 −2.75E−04 −6.40E−07 −2.11E−07 6.60E−09−1.23E−10 S14 0 −5.69E−05 −4.20E−07 −2.40E−08 3.84E−10 −5.71E−12

A zoom lens 10 c according to another embodiment including lenses L1-L8(with respective refractive power of negative, negative, positive,positive, negative, positive, negative, positive) is described belowwith reference to FIG. 3. The lens L5 and lens L6 are arranged togetheras one piece to form a doublet lens with a positive refractive power.The aperture stop 14 is located on the surface S12 of the lens L7 facingthe magnified side. The lens L8 is an aspheric lens and having a concavemagnified-side surface S14 and a convex minified-side surface S15crossed with the optical axis 12. In other embodiment, the lens L5 mayhave a positive refractive power and the lens L6 may have a negativerefractive power. In this embodiment, the aspheric lens is made fromglass. The detailed optical data of the zoom lens 10 c are shown inTable 7 and Table 8, and the aspheric surface data are shown in Table 9below.

TABLE 7 Surface Radius Interval Refractive Abbe number (mm) (mm) indexnumber Object description S1 52.76 1.00 1.49 70.2 lens L1(meniscus) S223.68 5.47 S3 90.65 1.00 1.49 70.2 lens L2(meniscus) S4 32.29 d1 S5−42.92 2.41 1.80 46.6 lens L3(meniscus) S6 −33.17 16.28  S7 26.68 2.051.95 32.3 lens L4(meniscus) S8 76.10 6.22 S9 −32.36 0.80 1.70 30.1 lensL5(biconcave) S10 9.76 4.32 1.88 40.8 lens L6(biconvex) S11 −32.26 2.15S12 −15.72 0.80 1.72 29.5 lens L7(biconcave) aperture stop S13 96.910.99 S14 −47.67 4.03 1.69 52.7 lens L8(aspheric) S15 −11.15 d2 S16 ∞cover glass surface d1 d2 wide 23.03 20.30 tele 16.37 21.18

TABLE 8 F/# EFL(mm) TTL(mm) wide 2.07 15.64 93 tele 2.14 17.15 87.23

In this embodiment, the total track length TTL is a distance along theoptical axis 12 measured from the surface S1 to the surface S16.

TABLE 9 K A B C D E S14 1.37E+01 −2.73E−04 −2.12E−06 −1.94E−07 1.39E−08−7.53E−10 S15 5.21E−02 −7.22E−05 −1.61E−06 −1.26E−08 5.71E−10 −5.32E−11F G S14 1.93E−11 −2.16E−13 S15 1.28E−12 −1.35E−14

A zoom lens 10 d according to another embodiment including lenses L1-L8(with respective refractive power of negative, positive, negative,positive, negative, positive, negative, positive) is described belowwith reference to FIG. 4. The lens L4 and lens L5 are arranged togetheras one piece to form a doublet lens with a positive refractive power.The aperture stop 14 is located between the lens L6 and the lend L7. Thelens L2 and the lens L8 are aspheric lenses, the lens L2 has a convexmagnified-side surface S3 and a convex minified-side surface S4 crossedwith the optical axis 12, and the lens L8 has a convex magnified-sidesurface S15 and a convex minified-side surface S16 crossed with theoptical axis 12. In other embodiment, the lens L4 may have a negativerefractive power and the lens L5 may have a positive refractive power.In this embodiment, the aspheric lens is made from glass. The detailedoptical data of the zoom lens 10 d are shown in Table 10 and Table 11,and the aspheric surface data are shown in Table 12 below.

TABLE 10 Surface Radius Interval Refractive Abbe number (mm) (mm) indexnumber Object description S1 28.56 3.50 1.70 55.5 lens L1(meniscus) S213.86 11.76  S3 622.36 3.05 1.53 56.0 lens L2(aspheric) S4 −457.17 d1 S574.78 0.50 1.49 70.2 lens L3(meniscus) S6 16.56 7.67 S7 34.56 6.00 1.8035.0 lens L4(biconvex) S8 −20.34 0.50 1.81 25.4 lens L5(meniscus) S9−171.56 15.87  S10 14.96 3.60 1.77 49.6 lens L6(biconvex) S11 −89.050.10 S12 ∞ 1.92 aperture stop S13 −44.22 0.50 1.70 30.1 lensL7(biconcave) S14 11.97 0.79 S15 20.33 2.47 1.50 81.1 lens L8(aspheric)S16 −26.89 d2 S17 ∞ cover glass surface d1 d2 wide 7.18 20.45 tele 1.0021.22

TABLE 11 F/# EFL(mm) TTL(mm) wide 2.03 15.75 88 tele 2.09 17.34 82.59

In this embodiment, the total track length TTL is a distance along theoptical axis 12 measured from the surface S1 to the surface S17.

TABLE 12 K A B C D S3 0 2.00E−05  8.91E−08 −4.92E−10 2.36E−12 S4 07.44E−07 0 −2.87E−10 0 S15 0 −1.70E−06  0 0 0 S16 0 5.86E−05 −3.46E−08 2.21E−09 1.93E−12

A zoom lens 10 e according to another embodiment including lenses L1-L8(with respective refractive power of negative, negative, positive,negative, positive, positive, negative, positive) is described belowwith reference to FIG. 5. The lens L3 and lens L4 are arranged togetheras one piece to form a doublet lens with a negative refractive power,and the lens L6 and lens L7 are arranged together as one piece to formanother doublet lens with a negative refractive power. The aperture stop14 is located between the lens L7 and the lens L8. The lens L8 is anaspheric lens and has a concave magnified-side surface S14 and a convexminified-side surface S15 crossed with the optical axis 12. In otherembodiment, the lens L3 may have a negative refractive power, and thelens L4 may have a positive refractive power. In this embodiment, theaspheric lens is made from glass. The detailed optical data of the zoomlens 10 e are shown in Table 13 and Table 14, and the aspheric surfacedata are shown in Table 15 below.

TABLE 13 Surface Radius Interval Refractive Abbe number (mm) (mm) indexnumber Object description S1 55.6 0.80 1.52 64.1 lens L1(meniscus) S222.8 4.26 S3 72.1 0.80 1.50 81.5 lens L2(meniscus) S4 30.7 d1 S5 198.74.41 1.82 46.6 lens L3(biconvex) S6 −26.8 1.54 1.56 58.3 lensL4(biconcave) S7 17.5 9.76 S8 22.3 4.70 1.77 49.5 lens L5(biconvex) S9−383.4 12.43  S10 16.3 3.78 1.66 57.4 lens L6(biconvex) S11 −14.3 0.801.73 28.3 lens L7(biconcave) S12 17.8 3.07 S13 ∞ 0.77 aperture stop S14−26.2 6.00 1.80 40.7 lens L8(aspheric) S15 −13.8 d2 S16 ∞ cover glasssurface d1 d2 wide 16.73 20 tele 10.39 20.97

TABLE 14 F/# EFL(mm) TTL(mm) wide 2.1 15.6 92 tele 2.17 17.2 86.63

In this embodiment, the total track length TTL is a distance along theoptical axis 12 measured from the surface S1 to the surface S16.

TABLE 15 K A B C D E F S14 2.23 −1.82E−04 −9.11E−07 −2.07E−08 −1.44E−102.10E−11 −4.54E−13 S15 8.39E−02 −4.09E−05 −8.77E−07 1.50E−08 2.90E−10−2.04E−11 2.45E−13

FIGS. 6-20 show optical simulation results of the zoom lens 10 a-10 e.FIGS. 6-10 respectively shows modulation transfer function (MTF) curvesof the zoom lens 10 a-10 e in the wide-angle position, where an abscissarepresents focus shift and an ordinate represents modulus of the opticaltransfer function (OTF). FIGS. 11-15 respectively shows MTF curves ofthe zoom lens 10 a-10 e in the wide-angle position, where an abscissarepresents spatial frequencies and an ordinate represents modulus of theOTF. FIGS. 16-20 respectively illustrate astigmatic field curves (withan abscissa unit of millimeter) and percentage distortion curves (withan abscissa unit of percentages) of the zoom lens 10 a-10 e underdifferent wavelengths of light of 460 nm (curves A and B), 550 nm(curves C and D) and 620 nm (curves E and F), where the symbol “S”indicates data values measured in a sagittal direction and the symbol“T” indicates data values measured in a tangential direction. Thesimulated results shown in FIGS. 6-20 are within permitted rangesspecified by the standard, which indicates the zoom lens 10 a-10 eaccording to the above embodiments may achieve good imaging qualities.

According to the above embodiments, the zoom lens may have at least onedoublet lens to balance chromatic aberration, and may have at least oneaspheric lens to reduce aberration. Besides, the zoom lens may have areduced number of total lenses and a large aperture stop. Further, thezoom lens may have a smaller value of EXP to reduce the total tracklength and thus is favorable for miniaturization, where Exp denotes adistance from an intersection to an image plane of a light valve, andthe intersection is formed by an optical axis of the zoom lens crossedby a chief ray emerging from a designated point of a periphery of thelight valve. In an optical projection system, the image plane of a lightvalve is typically located in an object side of an optical lens but notan image side for projection of the optical lens.

Accordingly, the zoom lens is featured with good correction ability,reduced size, and improved image qualities.

The foregoing description of the preferred embodiments of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform or to exemplary embodiments disclosed. For example, the designparameters listed in the tables 1-15 are merely for exemplifiedpurposes, but the invention is not limited thereto. Accordingly, theforegoing description should be regarded as illustrative rather thanrestrictive. Obviously, many modifications and variations will beapparent to practitioners skilled in this art. The embodiments arechosen and described in order to best explain the principles of theinvention and its best mode practical application, thereby to enablepersons skilled in the art to understand the invention for variousembodiments and with various modifications as are suited to theparticular use or implementation contemplated. It is intended that thescope of the invention be defined by the claims appended hereto andtheir equivalents in which all terms are meant in their broadestreasonable sense unless otherwise indicated. Therefore, the term “theinvention”, “the present invention” or the like does not necessarilylimit the claim scope to a specific embodiment, and the reference toparticularly preferred exemplary embodiments of the invention does notimply a limitation on the invention, and no such limitation is to beinferred. The invention is limited only by the spirit and scope of theappended claims. Moreover, these claims may refer to use “first”,“second”, etc. following with noun or element. Such terms should beunderstood as a nomenclature and should not be construed as giving thelimitation on the number of the elements modified by such nomenclatureunless specific number has been given. The abstract of the disclosure isprovided to comply with the rules requiring an abstract, which willallow a searcher to quickly ascertain the subject matter of thetechnical disclosure of any patent issued from this disclosure. It issubmitted with the understanding that it will not be used to interpretor limit the scope or meaning of the claims. Any advantages and benefitsdescribed may not apply to all embodiments of the invention. It shouldbe appreciated that variations may be made in the embodiments describedby persons skilled in the art without departing from the scope of theinvention as defined by the following claims. Moreover, no element andcomponent in the present disclosure is intended to be dedicated to thepublic regardless of whether the element or component is explicitlyrecited in the following claims.

What is claimed is:
 1. A zoom lens, comprising: a first lens group witha negative refractive power; a second lens group with a positiverefractive power, wherein each of the first lens group and the secondlens group moves individually; an aperture stop being disposed in andmovable with the second lens group; and a first doublet lens disposed ona first side of the aperture stop and between the first lens group andthe aperture stop, and a second side of the aperture stop being disposedwith at most two lenses including at least one aspheric lens.
 2. Thezoom lens as claimed in claim 1, wherein the aspheric lens is made fromglass.
 3. The zoom lens as claimed in claim 1, wherein an F number ofthe zoom lens is no more than 2.2
 4. The zoom lens as claimed in claim1, wherein a throw ratio of the zoom lens in a wide-angle position is inthe range of 1.3-1.6.
 5. The zoom lens as claimed in claim 1, whereinthe at least one aspheric lens has a first surface facing the aperturestop and a second surface opposite the first surface, the first surfaceis a concave surface crossed with an optical axis of the zoom lens, andthe second surface is a convex surface crossed with the optical axis ofthe zoom lens.
 6. The zoom lens as claimed in claim 1, wherein the firstlens group comprises two meniscus lenses with a negative refractivepower.
 7. The zoom lens as claimed in claim 1, wherein the first doubletlens has at least one lens with a positive refractive power and an indexof refraction of smaller than 1.68.
 8. The zoom lens as claimed in claim1, wherein a total number of lenses of the zoom lens is no more thanten.
 9. The zoom lens as claimed in claim 1, wherein the zoom lenssatisfies one of the following conditions: (1) the first lens groupcomprises two meniscus lenses with a negative refractive power, thesecond lens group comprises two lenses with a positive refractive powerlocated between the two meniscus lenses and the first doublet lens, andthe aspheric lens has a positive refractive power; (2) the first lensgroup comprises a meniscus lens with a negative refractive power and anaspheric lens, the second lens group comprises a meniscus lens with anegative refractive power located between the first lens group and thefirst doublet lens, and each aspheric lens in the first lens group andthe second lens group has a positive refractive power; (3) the firstlens group comprises two meniscus lenses with a negative refractivepower, the second lens group comprises a biconvex lens with a positiverefractive power and a second doublet lens, the biconvex lens and thesecond doublet lens are located between the first lens group and thefirst doublet lens, and the aspheric lens of the second lens group has apositive refractive power.
 10. The zoom lens as claimed in claim 1,wherein a zoom ratio of the zoom lens is in the range of 1.05-1.2, and aback focus distance of the zoom lens is in the range of 18-24 mm.
 11. Azoom lens, comprising: a first lens group and a second lens grouparranged in order along a direction, each of the first lens group andthe second lens group moving individually, the second lens group havinga first doublet lens, an aperture stop and an aspheric lens arranged inorder in a direction away from the first lens group, and the zoom lenssatisfying the condition: −26 mm≤EXP≤−28.5 mm, where Exp denotes adistance from an intersection to an image plane of a light valve, andthe intersection is formed by an optical axis of the zoom lens crossedby a chief ray emerging from a designated point of a periphery of thelight valve.
 12. The zoom lens as claimed in claim 11, wherein theaspheric lens is made from glass.
 13. The zoom lens as claimed in claim11, wherein an F number of the zoom lens is no more than 2.2
 14. Thezoom lens as claimed in claim 11, wherein a throw ratio of the zoom lensin a wide-angle position is in the range of 1.3-1.6.
 15. The zoom lensas claimed in claim 11, wherein the aspheric lens has a first surfacefacing the aperture stop and a second surface opposite the firstsurface, the first surface is a concave surface crossed with an opticalaxis of the zoom lens, and the second surface is a convex surfacecrossed with the optical axis of the zoom lens.
 16. The zoom lens asclaimed in claim 11, wherein the first lens group comprises two meniscuslenses with a negative refractive power.
 17. The zoom lens as claimed inclaim 11, wherein the first doublet lens has at least one lens with apositive refractive power and an index of refraction of smaller than1.68.
 18. The zoom lens as claimed in claim 11, wherein a total numberof lenses of the zoom lens is no more than ten.
 19. The zoom lens asclaimed in claim 11, wherein the zoom lens satisfies one of thefollowing conditions: (1) the first lens group comprises two meniscuslenses with a negative refractive power, the second lens group comprisestwo lenses with a positive refractive power located between the twomeniscus lenses and the first doublet lens, and the aspheric lens has apositive refractive power; (2) the first lens group comprises a meniscuslens with a negative refractive power and an aspheric lens, the secondlens group comprises a meniscus lens with a negative refractive powerlocated between the first lens group and the first doublet lens, andeach aspheric lens in the first lens group and the second lens group hasa positive refractive power; (3) the first lens group comprises twomeniscus lenses with a negative refractive power, the second lens groupcomprises a biconvex lens with a positive refractive power and a seconddoublet lens, the biconvex lens and the second doublet lens are locatedbetween the first lens group and the first doublet lens, and theaspheric lens of the second lens group has a positive refractive power.20. The zoom lens as claimed in claim 11, wherein a zoom ratio of thezoom lens is in the range of 1.05-1.2, and a back focus distance of thezoom lens is in the range of 18-24 mm.